The

Almost certainly Mandelbrot's The Misbehavior of Markets, a prophetic and readable challenge to the financial establishment's Gaussian assumptions — one that looked increasingly right after 2008. Mandelbrot and Hudson make the fractal critique accessible to educated general readers, not just mathematicians, which is a real achievement. The limitation is that the book tears down a model without building a usable replacement, so it's essential context rather than a practical guide.